Hi Nathanael,
You can’t automate the index of the sound that plays in a multisound, but you can do a few different things to get the same effect.
If you have 12 samples, just put them on one track, next to each other. This is a bit like the explosions/Single Explosion example in the example project in fmod studio, and it is controlled by the ‘size’ parameter.
You can use an event like that as a sound in another event, so it can look like a ‘sound’ in a track , this is done by using reference events (ie open 2 event windows, and drag an event into the track of another event).